This invention relates to industrial waste gas heat recovery devices and specifically to heat recuperators operative on hot waste gases heavy with particulate matter.
Heat recovery devices or recuperators have taken many forms depending upon the industries for which they have been used. A blast furnace pre-heat stove is a cylindrical structure containing a checker work of refractory brick. Waste blast furnace gases are passed through such a stove to heat the checker work. Ambient air is then passed through the hot stove to pre-heat the air before it is used in the blast furnace. Refractory checker work recuperators are also used in many other applications such as glass melting, and foundry soaking pit operations.
Ceramic tile recuperators and channel-type recuperators comprise banks of tubes, sometimes of uniform and sometimes of varying sizes. Often these tubes run between an input and output manifold. Hot gases pass through the tubes. Cold air is passed over the heated tubes for recouping the waste gas heat radiated therethrough.
Helical coil recuperators have been used in flue gas stacks. Such recuperators comprise a helically wound coil through which ambient air is passed for heating. The hot flue gases pass over this coil which is secured within the flow path of the hot gases. Radiation occurs through the walls of the ambient air-carrying coil.
One of the most popular types of stack or waste gas recuperators is the straight stack construction. This device passes waste gases through an inner tube while ambient air is passed through a surrounding jacket or tube. Heat from the waste gas is radiated through the separating wall to heat the ambient air.
A problem of scale, oxide and dirt build up occurs with each of these recuperators. This problem is magnified when the waste gases passing through the recuperator are particularly "dirty", i.e., heavily burdened with particulate matter. The dirt in the gas or the particulate matter entrained in the waste gas, deposits on the surfaces of the recuperator, thereby insulating the surfaces and substantially reducing the heat transfer capability, i.e., the capacity of the recuperator.
An object of the present invention is to provide a recuperator which is operable with particularly dirty waste gases having a cleaning function incorporated as part of the invention design for maintaining a stable heat transfer capacity for the recuperator.
Another object of the present invention is to provide a recuperator design where the waste gas pathway promotes the fall-out of heavier entrained particles for collection before the waste gas is scrubbed, filtered, etc.
Another object of the invention is to provide such a recuperator apparatus with the capability for leading of the waste gas passing through the recuperator with abrasive cleaning material, the recuperator having a forced waste gas pathway promoting separation of the entrained abrasive material, such separation causing an interaction with the surfaces of the recuperator whereby deposited dirt, scale and oxides are dislodged.
Another object of this invention is to provide an automatic recirculation of abrasive cleaning material through the recuperator.
A further object of this invention is to provide for an optional, automatic control of abrasive material concentration in the waste gas circulating through the recuperator.